Fertilizing Plants 101

Granular fertilizer for garden plants | Adobe Stock

Few gardeners are content to plant a garden and then relax while Mother Nature works her magic. We want to nourish, nurture, coddle, coax, even cajole small growing things into big, showy specimens. That takes fertilizer.

Most fertilizers contain a mix of nutrients plants need for healthy growth. The three numbers you see on the label refer to macronutrients, which contribute to overall healthy development while promoting lush green foliage or eye-popping blossoms. The numbers represent the percentage of three essential macronutrients: nitrogen, phosphorus, and potassium. A balanced fertilizer might have a 20-20-20 mix, while a mix intended to boost blossom production might be 10-52-10.

The fertilizer you choose at the start of the growing season will have a major impact on how your garden takes shape as it matures, especially when it comes to blooms on annuals and perennials. You want to choose and use fertilizer carefully for the best results.

The first number on the label always refers to nitrogen, which plays a starring role in promoting green, leafy growth. For most plants, nitrogen in a 10 percent to 12 percent range is ideal. A number in the low to mid-20s might be appropriate for elephant ears, coleus or sweet potato vine, where the point is showy foliage.

The second number always refers to phosphorus, which promotes blooming and fruiting. The higher the second number, the more abundant and lush the blossoms. When you really want to kick up flower production, look for at least 50 as a bottom line for phosphorus, and keep nitrogen down around 9 or 10. This kind of blossom booster is especially great for annuals or for a shy plant that needs a little nudge to produce bigger, showier flowers.

The third number refers to the percentage of potassium, which is responsible for your plants’ “muscle.” Potassium doesn’t contribute to dramatic visual impact, but if you want strong root development, disease resistance and overall vigor, look for 8 percent to 15 percent potassium.

Fertilizers also contain many micronutrients that are essential, but only in very small quantities for plant development. You don’t have to know what to look for — any quality fertilizer that lists nutrient composition will contain sufficient micronutrients Do not buy a fertilizer that has no ingredient list as “Guaranteed Analysis” is the term you want to look for to make sure you’re getting a quality product. Once you’ve determined which nutrient mix is right for your plants, the next question is, liquid or granular? Granular fertilizers release slowly into the soil, ensuring an even flow of nutrients over time. One application every two to three months is usually sufficient. It might be sprinkled on the soil around the plant, or later in the season, right on the mulch.

Fertilize more often in hot, wet weather — or if the growing season is especially cool and dry, you can stretch the span out to five or six months. Liquid fertilizers act quickly and need to be applied every week or two. Even if you choose granular, liquid can be a good choice for fast action. Say you want a gorgeous garden for a special occasion. Apply liquid fertilizer several days in advance, and you have the equivalent of giving your plants a shot of adrenaline.

No matter what fertilizer you choose, always follow directions on the label. More is almost certainly not better, and over-fertilizing can actually be toxic. Don’t hesitate to keep leftover fertilizer from one season to the next. Stored properly, it will have a long shelf life — just keep it cool and dry.